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Modes and functions of the ventilator
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Modes and functions of the ventilator

Views:5     Author:Site Editor     Publish Time: 2020-03-20      Origin:Site

1、 Main mechanical ventilation mode

Ventilator

(1) Interstitial positive pressure ventilation (IPPV): positive pressure in inspiratory phase and zero pressure in expiratory phase. 1. Working principle: the ventilator generates positive pressure in the inspiratory phase, presses the gas into the lung, when the pressure rises to a certain level or the inhaled capacity reaches a certain level, the ventilator stops supplying air, the expiratory valve opens, the patient's thorax and lung passively collapse, and produces exhalation. 2. Clinical application: all kinds of respiratory failure patients with ventilation function, such as COPD, etc.


(2) Intermittent positive and negative pressure ventilation (ipnpv): positive pressure in inspiratory phase and negative pressure in expiratory phase. 1. Working principle: the ventilator can work in both inspiratory and expiratory phases. 2. Clinical application: negative pressure of expiratory phase can cause alveolar collapse and iatrogenic atelectasis.


(3) Continuous positive airway pressure (CPAP): refers to the patient's artificial positive airway pressure during the whole respiratory cycle under the condition of autonomous respiration. 1. Working principle: the inspiratory phase is provided with continuous positive pressure air flow, and the expiratory phase is also provided with certain resistance, so that the airway pressure of the inspiratory and expiratory phases is higher than the atmospheric pressure. 2. Advantages: when inhaled, the continuous positive pressure air flow is greater than the inhaled air flow, so that the patient's inspiratory effort is saved, FRC is increased, and airway and alveolar collapse are prevented. It can be used for exercise before offline. 3. Disadvantages: large disturbance to circulation and large air pressure injury to lung tissue.


(4) IMV and IMV / SIMV 1. IMV: there is no synchronization device, the ventilator supply does not need the patient's spontaneous breathing trigger, and the time of each supply in the respiratory cycle is not constant. 2. SIMV: it has a synchronous device. The ventilator gives the patient mandatory respiration according to the designed respiratory parameters in each minute. The patient can breathe autonomously without the influence of the ventilator. 3. Advantages: give full play to the ability of self-regulation of respiration in offline; have less influence on circulation and lung than IPPV; reduce the use of seismostatic medicine to a certain extent. 4. Application: it is generally considered to be used when offline. When R < 5 times / min, it still keeps a good oxygenation state. Offline can be considered, and PSV is generally added to avoid respiratory muscle fatigue.


(5) Command ventilation per minute (MMV) 1. When autonomous respiration > preset minute ventilation, the ventilator does not command ventilation, only provides a continuous positive pressure. 2. When the autonomic breathing is less than the preset minute ventilation, the ventilator will give instructions to ventilate and increase the minute ventilation to reach the preset level.


(6) Pressure support ventilation (PSV) 1. Definition: under the premise of autonomous breathing, each inhale receives a certain level of pressure support, increasing the inhaled depth and amount of gas. 2. Working principle: the inspiratory pressure starts with the patient's inspiratory action and ends with the decrease of inspiratory flow rate to a certain extent or the patient's efforts to exhale. Compared with IPPV, the support pressure is constant and regulated by the feedback of suction flow rate; compared with SIMV, each suction can be supported by pressure, but the support level can be set according to different needs. 3. Application: SIMV + PSV: used for preparation before taking off line, which can reduce respiratory work and oxygen consumption 4. Indications: exercise ventilator; preparation before taking off line; ventilator weakness caused by various reasons; abnormal respiration caused by severe flail chest. 5. Precautions: generally not used alone, insufficient or excessive ventilation will occur.


(7) Volume support ventilation (VSV): each breath is triggered by the patient's autonomous respiration. The patient can also breathe without any support, and can reach the expected TV and MV levels. The ventilator will allow the patient to carry out real autonomous respiration, which is also suitable for preparation before offline.


(8) Capacity control of pressure regulation


(9) Working principle: P1 is equivalent to inspiratory pressure, P2 is equivalent to respiratory pressure, T1 is equivalent to inspiratory time, T2 is equivalent to expiratory time. 2. Clinical application: (1) when P1 = inspiratory pressure, T1 = inspiratory time, P2 = 0 or peep, T2 = expiratory time, it is equivalent to IPPV. (2) When P1 = peep, T1 = infinity, P2 = 0, T2 = O, it is equivalent to CPAP. (3) When P1 = inspiratory pressure, T1 = inspiratory time, p2-0 or peep, T2 = desired controlled respiratory cycle, equivalent to SIMV.


2、 Main mechanical ventilation function


(1) At the end of inhalation and before the beginning of exhalation, the ventilator does not supply air, and the exhalation valve continues to close for a period of time to keep the pressure in the lung at a certain level. 2. Clinical application: (1) prolonging the inspiratory time is beneficial to the gas distribution. (2) It is beneficial to the diffusion of gas (3) it is beneficial to the distribution and diffusion of atomized drugs in the lung (3) it can increase the burden on the heart.


(2)Positive end expiratory pressure ventilation 1. At the end of expiratory, the airway pressure did not drop less than 0, and still maintained a certain level of positive pressure. 2. Clinical application: it is suitable for hypoxemia caused by intrapulmonary shunt, such as ARDS 3. The mechanism of peep to correct ARDS (1) to reduce alveolar collapse and intrapulmonary shunt, correct hypoxemia caused by intrapulmonary shunt (2) to reduce alveolar collapse and increase FRC, which is conducive to the full exchange of gas on both sides of alveolar capillary. (3) The increase of alveoli pressure is beneficial to the diffusion of oxygen to capillaries. The alveoli are always in the state of expansion, which can increase the diffusion area of alveoli. (4) The increase of alveolar inflation can increase lung compliance and reduce respiratory work.


4.The main side effects of PEEP (1) influence on hemodynamics (2) barotrauma to lung tissue (3) can compress lung capillaries. Decreasing pulmonary blood flow may increase ineffective ventilation. (4) Can reduce alveolar surfactants.


5. Selection of the best PEEP: under the premise of maintaining FiO2 <60%, the minimum PEEP level of PaO2> 60mmHg can be achieved. 6. Endogenous PEEP: due to short expiration time or high respiratory resistance, gas retention in the alveoli can cause alveolar pressure to maintain positive pressure throughout the expiration cycle, which is equivalent to the effect of PEEP, which can be caused by disease or by Application of artificial respirator. (3) Prolonged exhalation and end-expiratory breath hold: suitable for patients with COPD and carbon dioxide retention. (4) Sigh: 1-3 deep breaths equivalent to 1.5 times to 2 times the tidal volume in every 50 to 100 breathing cycles. In order to periodically expand the alveoli at the bottom of the lungs that are prone to collapse, improve the timing of Gas exchange prevents atelectasis. (5) Inverse specific ventilation (IRV) Advantages: Extending the inspiratory time is conducive to the diffusion and distribution of the gas, and is conducive to correcting hypoxia. 2. Disadvantages: Large disturbance to the circulation and large barotrauma to the lung tissue.


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